1. Field of the Invention
The present invention relates to automatic door opening systems. More particularly, it pertains to an overhead door locking assembly that operates as part of a door opening system.
2. Description of the Prior Art
For large overhead doors that roll-up or swing-out, the use of automatic openers have become common. Such openers typically utilize a track mounted above the door for supporting a power-driven carriage. An elongated link arm connects the door to the carriage whereby the door will move in response to carriage movement.
Problems have been encountered in preventing unauthorized intrusion due to the inherent slack in the overall system. There is usually sufficient looseness in the various joints, the track/carriage/drive connections and the door construction itself, to permit wedging of the door bottom and unauthorized entry. Numerous mechanisms have been devised to overcome this problem.
In U.S. Pat. Nos. 3,435,558 and 3,526,994, a cam-operated latching mechanism is provided between the carriage and track means. This serves to prevent unwanted carriage movement, but does not address loose arm connections and inherent door flexure.
U.S. Pat. No. 2,589,479 avoids the above deficiencies with a sliding bolt lock. The bolt traverses the top edge of the door and engages a door frame keeper to stop unwanted raising of the door. While this is effective for roll-up panel doors, it requires a bell crank arm and associated parts making it cumbersome and costly. Further, it is actuated by a keyed outside handle which, can be accessed by an experienced intruder.
Door locks that automatically operate in conjunction with carriage movement are shown in U.S. Pat. Nos. 3,708,917; 4,442,631 and 4,597,224. Each of the above devices are distinguishable by the type of delay or lost-motion mechanism that is used to disengage the locks prior to door movement. In U.S. Pat. No. 4,597,224, the door arm comprises two sliding parts surrounded by the coils of a spring retained between opposing collars. Relative movement between the parts allows the carriage to unlock rocker latches prior to door movement.
In the aforementioned U.S. Pat. Nos. 3,708,917 and 4,442,631, a bell crank lever and rocker plate, respectively, are the mechanical means by which unlocking occurs before door movement. In each of the above cases, substantial changes to conventional systems are required. As such, retrofitting of existing door operating devices is not economically viable. Also, the patented mechanisms require carefully aligned pivot parts which further require properly tensioned spring means. Such assemblies inherently create upkeep and maintenance problems. Still further, they are costly to purchase and are not amenable for the average householder to install.